After prolonged rains, the gravel roads I sometime ride can be riddled with potholes. I don't let them interrupt the flow of my riding, and the result is the cases rattle hellaciously and eventually one or both of them will eject if the bike hits just the right hole at just the right speed. The last time this happened I extracted the case from a brook at the bottom of a steep bank. The case z-bracket latches are in good condition so I looked elsewhere for a solution.
Here's my prototype solution. I wanted something as simple to install and remove as the cases themselves so I didn't choose strapping.
Each tube is 225mm long. To prevent abrasion of the painted surface, place some duct tape or other protective tape along the lower surface of the cowl where the tube will make contact. I set them on top of the space between the case and frame then push them down until they bottom out on the case. They are removed easily by pulling them out using one finger. They slide a little fore and aft but haven't worked themselves significantly out of position. During this season, these anti-ejection devices have worked acceptably. The bike has hit potholes hard enough to eject a tube a couple of times but not the cases. I carry a two spares.
So far, this diameter has worked effectively. Trials continue.
